Thermostatic circuit breaker with contact arc prevention



Feb. 21, 1950 T. M. GUNN 2,498,039

THERMOSTATIC CIRCUIT BREAKER WITH CONTACT ARC PREVENTION Filed May 12, 1945 ,3 FIGS. 37 31 37 I I I I ,3 I VI Y O v shunt contacts I! and 2|.

Patented Feb. 21, 1 950 THERMOSTATIC CIRCUIT BREAKER WITH CONTACT ARC PREVENTION Townsend M. Gunn, Attleboro, Mass alslgnor to Metals and Controls Corporation, Attleboro, Mass, a corporation of Massachusetts Application May 12, 1945, Serlal N0. 593,406

5 Claims.

This invention relates to thermostatic circuit breakers and more particularly to such circuit breakers for across the line operation with contact arc prevention.

Among the objects of the invention are the provision of a circuit breaker which may be made small and compact; the provision of a circuit breaker for across the line operation adapted to interrupt heavy currents; the provision of a circuit breaker of the type indicated which may be easily calibrated during manufacture; the provision of a circuit breaker which has a long life; and, the provision of a circuit breaker which may be easily constructed of few and inexpensive parts. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing, in which one of various possible embodiments of the invention is illustrated,

Fig. 1 is a top plan of the device with the cover broken away;

Fig. 2 is a section taken on line 22 on Fig. 1;

Fig. 3 is a section taken on line 3-3 on Fig. 1 and showing the parts in different operating positions; and,

Fig. 4 is a section similar to Fig. 3 but showing the parts in still different operating positions.

Similar reference characters indicate corresponding parts throughout the several views of the drawing.

Referring now to the drawing, the circuit breaker of the present invention is shown in Figs. 1 and 2 in closed circuit position. The device includes a base I and a cover 3. Mounted in base I are terminals 5 and I which carry respectively stationary line contacts or terminals 9 and II. Mounted on bosses l2 on base I by means of bolts I3 are spring arms I5 and II which carry at their opposite ends, respectively, movable Spring arms I5 and I1 normally locate contacts I9 and 2| above contacts 3 and II, arm I5 biasing contact member I3 away from terminal 9 and arm I'I biasing contact member 2| away from terminal II. A hub 23 isformed on base I on which is mounted a snap-acting thermostatic disc 25 of the type shown and described in Spencer patent 1,448,240.

.Disc 25 is loosely mounted at its center by a pin 21 and carries at opposite points on its edge, disc or auxiliary contacts 23 and 3|. Pin 32 prevents rotation of disc 23 on pin 2! and locates contact 23 above contact I3, and contact 3| above contact 2|. A cavity 33 is formed in base I to accommodate a shunt resistance 35 connected between the two posts l3 which mount spring arms I5 and I1. Brackets 31 are mounted on base I and carry adjusting screw stops 33. Screws 33 are located above spring arms I5 and II to act as limiting stops therefor. Terminals 5 and I are connected respectively to power line leads 4| and 43.

When the device is in the position of Figs. 1 and 2, current passes through lead 4!, terminal 5, contact 9, sandwiched contact I3, contact 23, disc 25, contact 3 I, sandwiched contact 2| contact I I, terminal I and lead 43. Resistance 35, which is of a relatively high value, is at this t me in shunt or parallel around disc 25 (see parts I5, II, I3 and 35).

v If the current passing through the device increases to an undesirably high value, the passage of the current through disc 25 heats it until it snaps from its non-overload position bowed toward terminals 3 and I I, as shown in Fig. 2, to its overload position bowed away from the terminals, as shown in Fig. 4, passing through the stage shown in Fig. 3. The resilient force of disc 25. which in its Fig. 2 position sandwiched contact I3 between contacts 9 and 23, and contact 2| between contacts II and 3|, is removed by this change in curvature. The resilience of arms I5 and I1 thereupon separates contact I3 from contact 9 and contact 2| from contact I I. Theparts momentarily assume the positions shown in Fig. 3 in which the contacts I3 and 2| momentarily follow contacts 23 and 3| respectively. This condition continues until the stops 33 are reached by the spring arms I5 and I1. The disc 25 then continues to move, thereby advancing the contacts 29 and 3| away from the contacts I9 and 2 I, respectively (Fig. 4). In the Fig. 3 position current may tend to are from 3 and II to I9 and 2|, respectively, and then pass partly through the disc and partly through the resistance. As the contacts 23 and 3| first separate from contacts I9 and 2|, respectively (under the Fig. 4 conditions) and before ionization takes place between them, the resistance is high in the disc part of the parallel arms of the circuit con tituted by the disc 25 and the resistance 35.

The current path is thereby established through resistance shunt 35. Thus little or no arcing occurs between contacts I3 and 29 and 2| and 3|. respectively. The high value of resistance 35 3 also inhibits arcing between contacts 8 and It and II and 2|, respectively. Thus the device assumes the position shown in Fig. 4, the circuit between lines 4| and 43 having been broken with little or no arcing taking place between any pair of contacts. In this connection it should be noted that, in addition to the advantageous mechanical functions asserted above for a given group of cooperating contacts such as 9, I9, 29 or ll, 28, 8t, substantially simultaneously compounding the functions of both in electrical series (relative either to the resistance 35 or disc 25)" results in further reducing the tendency to are formation.

The position of stops 39 is adjustable to vary the relative separation between contacts 9 and i9, and It and 2| on one hand and between contacts 49 and 29, and 2| and 3| on the other.

Contacts l9 and 2| may be made large in size, if desired to act as are coolers and further to tend to snuff out any arcs which may form.

In the drawing the circuit breaker is shown as or the automatic type. Disc 25 is constructed so that after the circuit is interrupted disc 25 cools and snaps back to its Fig. 2 position. This again sandwiches contact :9 between contacts Q and 29 and contact 2i between contacts it and ill, reclosing the circuit first described above. It the fault in the circuit which caused the passage oi the undesirably high current through disc 25 still exists, the above described cycle will be repeated until the fault is corrected.

If a manual resetting circuit breaker is desired, disc 25 is merely constructed with a difierent temperature difierential so that it does not snap back to its Fig. 4 position upon cooling to normal ambient temperature, but must be manually pushed to its Fig. 2 position. A handle is then located in cover 3 above disc 25 so as to press on the edges of disc 25.

The circuit breaker of the present invention may be used to interrupt currents of a thousand amperes or over without substantial danger to the contacts. Currents of such sizes are normally highly disruptive of circuit breaker contacts be= cause of arcing between the separated contacts. The circuit breaker of the present invention, on the other hand, practically eliminates arcing between any pair oi the contacts, and therefore the contacts may be made smaller than would other wise be possible. Moreover, inhibition of arcing makes it possible to use the circuit breaker for long periods of time without repair or replacement.

The circuit breaker of the present invention may be used in lieu of fuses to protect house lighting circuits. If an automatic circuit breaker such as described herein is employed, the breaker needs no attention and has a long period of usefulness. If the breaker of the present invention is made to require manual resetting it still avoids the necessity for replacing burnt out fuses, which may not be readily available.

Accordingly it will be seen that a circuit breaker is provided which breaks a circuit by first switching in a shunt circuit and then switching itself and the protecting shunt circuit out of the line to open the circuit.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in acoaoco d the accompanying as shall be interpreted as illustrative and not in a-limiting sense.

I claim:

1. A thermostatic circuit breaker comprising line terminals for connecting the circuit breaker in a line, a contact member movable toward and away from one of said terminals and biased away from said one terminal, an electrically conductive, thermostatically actuable element movable from a non-overload to an overload position in response to current overload in the line, said element in its non-overload position engaging and holding said contact member against said one terminal and completing a circuit from one side of the line through said contact member and element to the other side of the line, said el..=- ment moving away from said one terminal in moving to its overload position, an electrical re= sistance connectible with the other side oi the line through said contact member, and a stop positioned to limit movement of the contact mein= her away from said one terminal for disengage= ment of said contact member and electrically conductive element when the latter moves to its overload position.-

2. A thermostatic circuit breakercomprising line terminals for connecting the circuit breaker in a line, a contact member rnovable toward and away from one of said terminals and biased away from said one terminals, a snap-acting, electri cally conductive thermostatic element adapted to snap from a non-overload to an overload posh tion upon heating in response to flow or" overload current therethrough, said element in its non overload position engaging and holding the contact member against said one terminal and com= pieting a circuit from one side of the-line through said contact member and element to the other side of the line, said element moving away from said one terminal in moving to its overload pcsiticn, an electrical resistance connectible with the other side of the line through said contact mezn= ber, and a stop positioned to limit movement of the contact member away from said one terminal for disengagement of said contact member and electrically conductive element when the latter moves to its overload position.

3. A thermostatic circuit breaker comprising e terminals for connecting the circuit breaker in a line, contact members movable toward and away from the terminals and biased away from the terminals, an electrically conductive, thermostatically actuated element movable from a non-overload to an overload position in response to current overload in the line, said element in its non-overload position engaging and holding said contact members against the terminals, said element moving away from the terminals in moving to its overload position, an electrical resistance connecting the contact members, and

stops positioned to limit movement of the contact members away from the terminals for disengagement of the contact members and element when the latter moves to its overload position.

4. A thermostatic circuit breaker comprising a base, a pair of line terminals on the base, a pair of contact members mounted on the base for movement toward and away from the respective terminals and biased away from the terminals, a snap-acting, electrically conductive themestatic element adapted to snap from a non-overload to an overload'position upon heating in re= spouse to passage of overload current therethrough, said element being mounted on the base 76 in-such relation to the terminals and contact members as to engage the contact members and hold them against the terminals when in its nonoverload position, thereby to complete a circuit between the terminals, said element moving away from the terminals to release the contact members upon snapping to overload position, an electricalresistance connecting the contact members, and stops mounted on the base positioned to engage the contact members and limit their movement away from the terminals for disengagement of the contact members and thermostatic element when the latter has snapped to overload position.

5. A thermostatic circuit breaker comprising a base, a pair of line terminals fixed on the base, a pair of spring arms mounted on the base carrying contacts movable toward and away from the respective terminals, the arms tending to move the contacts away from the terminals, a snapacting, dished thermostatic disc mounted on the base having a pair of contacts engageable with the movable contacts, said disc being electrically conductive and adapted to snap from a nonoverload position bowed toward the terminals to an overload position bowed away from the terminals upon heating in response to passage of overload current therethrough, said disc being located on the base for engagement of its contacts with the movable contacts to hold them against the terminals when the disc is in nonoverload position, and for releasing said movable contacts upon snapping to overload position, an electrical resistance connecting said movable contacts through said spring arms, and a pair of stops mounted on the base in position to engage the spring arms to limit their movement away from the terminals for disengagement of the movable contacts and the contacts on the disc when the disohas snapped to overload position.

TOWNSEND M. GUNN.

REFERENCES CITED The following references are of record in the file of this patent: 

